As is known in the dental treatment, for example, in the case that teeth are missed or damaged, the denture is often set for the patient. At first, the dentist make an oral impression-taking of the mouth and then accordingly the dental plaster cast is produced. This cast is completely reproduced of the patient mouth: soft tissue(gingiva), healthy remaining teeth standing from the gingiva and edentulous areas made by damage or injury. Using this plaster cast, for example, the denture is made for the edentulous areas of the patient.
The above mentioned denture, for example showed in FIG. 8 (in the case of wire-clasps), is consist from the artificial teeth (FT) and the denture base (RF). This type of denture is produced to hold the adjacent healthy remaining teeth (named clasped tooth : ST) by using clasp C, for example, wire-clasp or cast-clasp to get the resistant force against removing. For the denture, it is very important to design the clasps and the denture base for smooth and natural setting.
The above mentioned clasp used in the dental treatment is mainly devided into the wire-clasp which is, for example, made by bending the ready-made metal wire of a diameter about 1 mm and the cast-clasp which is made by casting the wax pattern, for example, with Co--Cr alloy, Pt--Au alloy, Au alloy, Pd alloy and so on.
Showing in FIG. 8B and FIG. 8C, for example, clasp C is consisted from the curved portion AP (called the clasp arm portion AP) which is fitted to the undercut surface of adjacent healthy remaining teeth ST and the leg-portion LP which is bedded into resin base RF.
As you make denture, it is important to design the denture-base and clasps. This designing is to draw the outline of the denture-base and clasps composed the denture on the dental plaster cast. When you design clasps, if you don't make a enough observation of the tooth contour, the produced denture has verious troubles caused from the amount of undercut: for example, difficult to insert into the mouth, or not enough resistant force against removing and bracing after setting brings to take out too easy. Therefore, in designing the clasps and the denture-base, drawing of the outline of clasps on the dental plaster cast is very important and accordingly gives the great effect to the efficiency for denture producing processes and decides the quality of denture.
In the usual designing method of the denture, the usual surveyor apparatus which is representative of the NEY surveyor apparatus is used. This usual type of surveyor apparatus is composed with the surveyor table which can adjust and fix the direction of denture designing for the dental plaster cast and the survey line drawing device which holds the drawing lead material vertically. The methods of survey line drawing with the usual surveyor are following:
First, the dental plaster cast is fixed on the surveyor table and the path of insertion of the denture is decided. Then shown in the FIG. 14A and FIG. 14B, the survey line 80 (survey line is the line connecting the greatest circumference of tooth or tissue which is drawn on the cast by using the vertical drawing shaft like a pencil lead. It is called the survey line A which is drawn as the reference line to know the undercut area for the direction of designing. And it is called the survey line B which is drawn to get the outline of the clasp by tilting the Y axis and the X axis for the direction of designing. And It is called the survey line K which is drawn to get the outline of the base by tilting the X axis and the Y axis. After now, it is called separately the survey line A,B and K.) is drawn on the dental plaster cast with the survey line drawing tool (In this case, the line is called the survey line A.). And using the undercut guage, amounts of undercut is measured according to the elasticity of clasp-material the clasp, and the measured point V is decided as the terminal portion of clasp. Then, for the clasp arm portion AP, the outline is drawn by hand depending on the empirical knowledge and intuition. The outline of the denture base is also drawn in the same way.
Usually, in designing the Akers-type clasp, as shown in FIG. 14A for the case of wire-clasp, 2/3 of the opening terminal side of the clasp arm is designed to set into the undercut area. However, the denture produced in this way has problems functionally in the mouth, for example, low stability against the horizontal movement and less-resistance against for the lift-up movement of the prosthetic side. These problems are caused from the reason that the curved arm portion AP of clasp C affects holding effect for the clasped tooth ST mainly only with the terminal portion of clasp. This problem is not solved by using bigger undercut amount and deciding the measured point V'. It is necessary to design the clasp with longer undercut portion and holding the clasped tooth ST as shown in FIG. 14B, and get a high resistant force against the various working directions.
In the case of wire-clasp shown in FIG. 14B, the method which the clasp arm is inserted into undercut portion from the less-elastic portion near the clasp body to the clasp tip is introduced as "YAZAKI clasp" in the book of "Wire-Clasp" by Seiji Kawabe, but in this method, the outline of clasp is drawn depending on the empirical knowledge and intuition, so the resistant force of each clasps may not be uniform and sometime happen the problem which can not be inserted for the reason of tightness. In the new designing method of introducing now, the clasp arm is also inserted into undercut area from the portion near the clasp body like as YAZAKI clasp, but the survey line B is drawn using surveyor (83' in FIG. 7) and this survey line B is used for designing the outline of clasp. By making a rule of drawing the survey line, it is possible to design the clasp which has uniform resistant force and is easy to insert for any kinds of cases.
About this invention, one more invention of the surveyor apparatus for clasp designing is known in Japanese Laid-Open Patent Publication No.47,089 of 1995 (official report) invented by the same person (called the formar invention). This former invented apparatus has the structure being able to drow the survey line B by rotating two axis of the X and the Y and giving the inclination to the cast, but this time new improvement is added. In the clasp designing surveyor apparatus of the former invention, the surveyor table is controlled only with the two rotary axis of X-axis and Y-axis, and it has the problem to happen errors for the angle setting when either of the X-axis or Y-axis is inclined.
Then, it is mentioned about the improvement of the structure to dissolve the angle setting error happened in the former invention. As shown in FIG. 9C, in the former invention, the relation of the rotary axis and the cast is consisted with the Y1-axis, the X1-axis and the dental plaster cast setting device. On the other hand, in this invention, as shown in FIG. 9A, the first component has the relation of the Y1 axis, the X1 axis, the Z axis, the universal joint mechanism and the dental plaster cast setting device. As shown in FIG. 9B, the second component has the relation of the Y1 axis, the X1 axis, the Z axis, the Y2 axis, the X2 axis, the universal joint mechanism and the dental plaster cast setting device.
The new surveyor apparatus is composed with the axis which has the rotary axis of the Z axis extending vertically at the cross point of the rotary axis of the X1 axis and the Y1 axis, the X2 axis and the Y2 axis which is extended vertically for the Z rotary axis and is the same direction for the X1 axis and the Y1 axis, the universal joint which is extended vertically at the cross point of the rotary axis of the X2 axis and the Y2 axis, and the dental plaster cast setting plate which is on the universal joint.
Then, in this designing method for the denture, the items needed for angle setting is listed.
(a) the angle setting for the direction of the basic designing. PA0 (b) the angle setting for the clasp designing. PA0 (c) the angle setting for the denture base designing. PA0 (a) The angle setting for basic designing direction setting. PA0 (b) The angle setting for clasp designing. PA0 (c) The angle setting for denture base designing.
In the former invention, the above three angle setting is made with only the Y1 axis and the X1 axis, therefore the angle error happens when the additional angle setting is needed with the inclined axis of either the X axis or the Y axis after the first angle setting.
And in the former invention, above (c) item is not mentioned. In this invention, each needed angle setting is able to do independently. And more, the angle setting for the denture base designing is newly proposed.
The main role of each axis of this invention is mentioned (shown in FIG. 9 and FIG. 10).
It is setted with the universal joint mechanism 12.
It is setted with the X1 axis, the Y1 axis and the Z axis, or with the X2 axis, the Y2 axis and the Z axis,
It is setted with the X1 axis, the Y1 axis and the Z axis, or with the X2 axis, the Y2 axis and the Z axis.
This inventional apparatus do not happen the error when the designing for the denture base and the clasp is made separately after the basical designing direction setting, it is differ from the former invention. So, this surveyor apparatus is able to design the denture which is aesthetic and has clasps with suitable resistant force for verious working direction.
Untill now the designing direction for the denture base and the clasp is made only with the same direction, but in this invention shown in FIG. 15, the situation untill the clasp arm AP reach to touch to the surface of the clasped tooth is considered as the designing direction E of the denture base, and the situation after that till the denture is inserted on the mucous membrane is considered as the designing direction F of the clasp. By this designing method that the designing direction of the clasp and the base are divided individually, it is possible to design the denture which the denture base and the bar are bedded into the deep undercut area shown in FIG. 13.
Further, this invention provides the surveyor apparatus which the pencil shaft for the survey line drawing device (shown in FIG. 6 and FIG. 12) is removable type and enable to sharpen the pencil rod quickly and enable to change easily the drawing holder with another color pencil rod or measuring rod, so brings higher working efficiency.